When using four-valve cylinder heads having two intake valves and two exhaust valves per cylinder, the timing is more complicated than in the case of two-valve cylinder heads. In the latter, the injector is at an angle to the cylinder axis, and the two valves can be disposed at the center of the cylinder head. In contrast, in the case of four-valve cylinder heads, the aim is to mount the injector vertically, and to distribute the four gas-exchange valves around the injector two parallel to each other. In the four-valve cylinder head, the valve seats need to be optimized in terms of position and size, and the rocker arm pushrods are disposed on the “cold” intake side of the cylinder head. As a result, the installation of the rocker arm bearing becomes much more difficult because the valve spring clearances reduce the size of the rocker arm seating.
German Patent Publication DE-AS 11 79 764 describes a valve control system for an internal combustion engine having two intake valves and two outlet valves per cylinder, where the equidirectionally acting arms of the two rocker arms have different lengths, and the arms of each rocker arm lie in a plane perpendicular to its pivot axis, which is disposed at an angle to the longitudinal central plane of the internal combustion engine. Given a suitable arrangement of the control shaft and of the intake and exhaust pipes relative to each other, the above-described measures make it possible to obtain a wear-resistant valve control system with a minimum of effort. While this rocker arm design eliminates the wear-promoting transverse forces, this manner of mounting markedly increases the ratio between the lift of the valve and the lift of the lifter, which corresponds to an increase in forces and in the Hertzian stress between the cam and the lifter, whose magnitude is one of the determinants of the durability of the components concerned. Since the contours of the rocker shaft, and consequently also that of the bearing bolt, extend beyond the cylinder head, vibration-free mounting of the pedestal on or to the cylinder head is very complex and requires additional reinforcement of the cylinder head at the mounting points, especially at the point near the exhaust port and at the point near the intake port.
German Patent Publication DE 3637199 discloses a rocker arm bracket which is composed of at least three different separate parts.